1. Field of the Invention
The present invention generally relates to an adhesive composition, and particularly to an adhesive composition which has good adhesive strength, stability, over a wide temperature range, and resistance to naphthenic oils and plasticizers.
2. Description of the Prior Art
A prior art adhesive composition containing a nitrile rubber with carboxyl groups is composed of 100 parts of Hycar-1072 (Trade Name by Goodrich Co., Ltd.) and from 20 to 50 parts of either an alkyl-phenol resin or a vinylchloride-vinylacetate copolymer. Hycar-1072 is a nitrile-butadiene rubber with carboxyl groups. This Hycar-1072 is dissolved in a solvent, together with an alkyl-phenol resin or the like, to prepare a rubber solution. Thereafter, the thus prepared rubber solution is coated on, for example, a polyethylene film, and the coating is dried. Then, the resulting polyethylene film is laminated to a polyvinylchloride film and thereafter the polyethylene film is stripped therefrom to produce a polyvinylchloride sheet with an adhesive layer thereon. However, the adhesive force of this adhesive layer to such polyvinylchloride sheet is generally low; particularly at relatively high and low temperatures. Thus, for example, when the temperature is decreased to -10.degree.C., the adhesive force becomes almost zero, and when the temperature raised to 80.degree.C., the adhesive force is decreased to about 0.6Kg/2cm, when an adhesive layer is laminated to an aluminium foil.
In addition, when such a prior art adhesive composition is laminated to, for example, polyvinylchloride film, phthalates which are compounded in the polyvinylchloride film as a plasticizer, undesirably become dissolved in the alkyl-phenol polymer which is contained in such adhesive composition and, also, the polyvinylchloride film becomes undesirably contracted at the places where such phthalates are so removed therefrom by such dissolution. The result is a deterioration in adhesive characteristics between such adhesive layer and such polyvinylchloride film.
A prior art adhesive composition comprised of polyamide resins derived from polymeric fatty acids and alkylene polyamines is described in U.S. Pat. No. 2,955,951 and U.S. Pat. No. 3,444,026, and a method of making polyamide resins similar to those used in this invention is described in U.S. Pat. No. 3,396,180 and U.S. Pat. No. 3,408,317.
Above mentioned polyamide resin compositions, have a good adhesive characteristic at ambient temperatures but have unsatisfactory adhesive bond strength at both relatively low and relatively high temperatures.